Juvenile Neuronal Ceroid Lipofuscinosis (JNCL) is a neurodegenerative lysosomal storage disease caused by an autosomal recessive mutation in CLN3. Symptom onset occurs between 5-10 years of age with blindness and intractable seizures, followed by progressive cognitive and motor deterioration, and premature death (late teens-early 20s). JNCL is typified by neuronal apoptosis; however, neuronal death in the CLN3?ex7/8 mouse model occurs later in the disease process (12 months) compared to astrocyte activation, which is an early event (1-3 months) and predicts regions of eventual neuronal loss. Our preliminary data reveal reduced Ca2+ signaling, glutamate transporter, and glutamine synthetase expression in CLN3?ex7/8 astrocytes, which manifests as impaired glutamate clearance. This is expected to influence neuronal apoptosis, since excessive extracellular glutamate has been implicated in neuron excitotoxicity during JNCL. This suggests that aberrant astrocyte activity may impact neuronal dysfunction and late- stage apoptosis, which mandates a systematic assessment to alleviate this confound and separate the cell autonomous contributions of CLN3 mutation in neurons vs. astrocytes. To this end, our group has developed novel self-complementary (sc) adeno-associated virus 9 (scAAV9) constructs to probe cell type-specific effects of CLN3 action, where human CLN3 (hCLN3) is preferentially targeted to neurons (synapsin-hCLN3), astrocytes (GFAP-hCLN3), or both populations using the methyl-CpG-binding protein 2 (MeCP2) promoter (MeCP2-hCLN3) to examine effects on disease mechanisms and pathology. We will utilize these viruses as tools to test the hypothesis that neuron loss in JNCL is influenced by distinct cell autonomous actions of CLN3 in neurons and astrocytes. The effects of cell type selective CLN3 expression on disease attributes will be examined in the following Specific Aims: 1) Examine the effects of restoring CLN3 expression in neurons vs. astrocytes on behavioral, pathological, and physiological deficits in JNCL; 2) Examine the effects of CLN3 mutation in neurons vs. astrocytes on neurotransmitter perturbations in JNCL; and 3) Examine cell autonomous effects of CLN3 on proteostasis. This work will be the first to directly demonstrate cell autonomous effects of CLN3 mutation and how this contributes to neuronal loss in JNCL. This would significantly expand our understanding of the major cell types driving neuropathology and delineate how/where therapies should be targeted to exert the greatest impact on JNCL pathogenesis.